X-ray imaging techniques are widely applied in the security inspection field. Generally, X-rays are generated by utilizing electron beams provided by an electron accelerator to impinge on an electronic target. However, only a small portion of the generated X-rays is used for imaging. As such, at the time of X-ray imaging, it can easily occur to people to generate photoneutrons by way of X-rays impinging on a photoneutron target for the purpose of object imaging by means of transmission of photoneutron through the object. Since the behavioral property of photoneutrons in the object is different from that of X-rays, recognition of the object can be improved using two different imaging techniques.
However, photoneutrons are generated together with a large number of X-rays such that the measurement of photoneutrons will be interfered by X-rays, so it is infeasible to measure the photoneutrons by way of fast neutron detection directly. Photoneutrons must be moderated and then measured by a thermal neutron detector. Position information of the photoneutron rays has to be obtained upon imaging by means of photoneutron transmission. Generally speaking, position information of the rays depends on the size and position of the detector. However, during moderation of the photoneutrons, the photons have been diffused and the position information thereof has been lost when the photons had finally been measured. In this case, imaging is impossible. The present invention provides a solution to this problem so as to obtain a two-dimensional imaging of the detected object using the photoneutrons.